Uncalcined Hydroxyapatite Research Articles

Comparative In Vitro Dissolution Assessment of Calcined and Uncalcined Hydroxyapatite Using Differences in Bioresorbability and Biomineralization.

This study reports the effect of the not-calcining process on the bioresorption and biomineralization of hydroxyapatite through in vitro dissolution assessment. The prepared calcined hydroxyapatite (c-HAp) and uncalcined hydroxyapatite (unc-HAp) have a particle size of 2 μm and 13 μm, surface areas of 4.47 m2/g and 108.08 m2/g, and a Ca/P ratio of 1.66 and 1.52, respectively. In vitro dissolution assessments of c-HAp and unc-HAp were performed for 20 days at 37 °C in a citric acid buffer according to ISO 10993-14. During the dissolution, the c-HAp and unc-HAp confirmed an increase in weight, and the calcium and phosphorous ions were rapidly released. The calcium ions released from c-HAp formed rod-shaped particles with a longer and thinner morphology, while in unc-HAp, they appeared thicker and shorter. In the ICP-OES results, the concentrations of calcium elements were initially increased and then decreased by this formation. The rod-shaped particles identified as calcium citrate (Ca-citrate) through the XRD pattern. The calcium content of Ca-citrate particles from unc-HAp was higher than that from c-HAp. The unc-HAp demonstrated non-toxic properties in a cytotoxicity evaluation. Therefore, due to its higher bioresorption and biomineralization, unc-HAp exhibits enhanced biocompatibility compared to c-HAp.

Effect of pH on the In Vitro Biocompatibility of Surfactant-Assisted Synthesis and Hydrothermal Precipitation of Rod-Shaped Nano-Hydroxyapatite.

Given their wide range of biomedical applications, hydroxyapatite (HA) nanoparticles are an attractive material widely used in many fields. Therefore, a simple, inexpensive, and stable process for the synthesis of HA nanoparticles is necessary to meet current needs. Herein, we studied HA synthesis assisted by four surfactants, namely cation, anion, non-ionic, and zwitterion templates, to verify the synthesis phase, aspect ratio, morphology, and biocompatibility under different environments (i.e., pH 4 and 9) before and after calcination. Results showed that before calcination, the surfactant-free groups could not produce HA but showed an abundant dicalcium phosphate anhydrous (DCPA) phase at pH 4. Except for the anionic group containing a small amount of DCPA, all surfactant-assistant groups presented single-phase HA in acidic and alkaline environments. The diameter of HA synthesized at pH 4 was significantly larger than that of HA synthesized at pH 9, and the effect of aspect ratio changes after calcination was more significant than that before calcination. The uncalcined rod-shaped HA synthesized with a non-ionic template at pH 4 demonstrated excellent cell viability, whereas anionic, cationic, and non-ionic surfactants exhibited biocompatibility only after calcination. At pH 9, non-ionic and uncalcined zwitterion-assisted rod-shaped HA showed excellent biocompatibility. In conclusion, the uncalcined HA rod-shaped nanoparticles synthesized from the non-ionic template at pH 4 and 9 and the zwitterion template at pH 9, as well as all surfactant-assisted HA after calcination, had no cytotoxicity. These tailor-made non-toxic HA types can meet the different requirements of apatite composite materials in biomedical applications.

Enhanced fluoride removal from drinking water using non-calcined synthetic hydroxyapatite

Elevated level of fluoride in groundwater is a concern for human health in developing countries. This study presents the advantage of synthetic un-calcined hydroxyapatite over calcined hydroxyapatite for fluoride removal. The synthesized hydroxyapatite (HAP) was characterised using XRD, FEG-SEM, and XPS. The effect of HAP’s calcination temperature was evaluated on fluoride removal. It was observed that fluoride uptake decreases with increasing calcination temperature. The fluoride uptake capacity of un-calcined HAP was found to be 4.38 mg F−/g HAP, whereas it was 3.53 mg/g for HAP calcined at 300 °C and further reduced to 0.7 mg/g for HAP calcined at 800 °C. Equilibrium studies revealed that fluoride uptake by HAP is best described by Langmuir isotherm and fluoride removal follows pseudo-second-order reaction kinetics. The defluoridation capacity decreased with an increase in pH (pH 5–9). Further studies revealed that HAP dose of around 2.5 g/L can effectively reduce fluoride to below 1 mg/L from groundwater having an initial fluoride concentration of 10 mg/L. Continuous flow column studies were also performed as a packed bed reactor mode of operation is preferred in a real-life scenario. The obtained results follow a conventional bed depth service time (BDST) model, hence un-calcined HAP packed bed reactor can be designed based on the BDST model to provide safe drinking water to the people at risk.

Vertical ridge augmentation using a porous composite of uncalcined hydroxyapatite and poly-DL-lactide enriched with types 1 and 3 collagen

BackgroundPrevious studies have shown that porous composite blocks containing uncalcined hydroxyapatite (u-HA; 70 wt%) with a scaffold of poly-DL-lactide (PDLLA, 30 wt%) are biodegradable, encourage appropriate bone formation, and are suitable for use as a bone substitute in vertical ridge augmentation. The present study aimed to accelerate osteogenesis in vertical ridge formation by adding types 1 and 3 collagen to the u-HA/PDLLA blocks and assessing the effect.Material and methodsThe bone substitute in the present study comprised porous composite blocks of u-HA (70 wt%) with a PDLLA (27–29 wt%) scaffold and enriched with types 1 and 3 collagen (1.7 ~ 3.4 wt%). The control blocks were composed of u-HA (70 wt%) and PDLLA (30 wt%). The materials were formed into 8-mm diameter, 2-mm high discs and implanted onto the cranial bones of six rabbits. The animals were sacrificed 4 weeks after implantation, and histological and histomorphometrical analyses were performed to quantitatively evaluate newly formed bone.ResultsNew bone formation occurred with both block types, showing direct contact with the original bone. Mean ± standard deviation bone formation was significantly greater in the experimental blocks (25.6% ± 4.8%) than in the control blocks (17.0% ± 4.7%).ConclusionsHistological and histomorphometrical observations indicated that new bone was formed with both block types. The u-HA/PDLLA block with types 1 and 3 collagen is a more promising candidate for vertical ridge augmentation than the u-HA/PDLLA alone block.

Preparation and characterization of porous hydroxyapatite pellets: Effects of calcination and sintering on the porous structure and mechanical properties

In this study, porous hydroxyapatite structures were produced by using urea particles of 600–850 µm size. Samples with two different urea composition (25 and 50 wt%) were prepared along with samples without any urea content by adding urea to commercially available hydroxyapatite in its as purchased and calcined states. The produced pellets were sintered at 1100 ℃ and 1200 ℃ for 2 h. Compression tests and microhardness measurements were conducted and changes in density values were examined in order to determine the effect of the calcination state of the prior hydroxyapatite powder, the sintering temperature and the amount of urea added. Also X-ray diffraction, Fourier transform infrared, and scanning electron microscopy analyses were conducted to determine the phase stability, functional groups, and pore morphology, respectively. Calcination is found to negatively affect the densification and sinterability of the produced samples, resulting in a decrease of compressive strength and microhardness. With the control of the urea content and sintering temperature uncalcined hydroxyapatite can successfully be used to tailor the density and mechanical properties of the final porous structures.

The Use of Porous Composite Uncalcined Hydroxyapatite / poly-DL-lactide for Vertical Ridge Augmentation

The Use of Porous Composite Uncalcined Hydroxyapatite / poly-DL-lactide for Vertical Ridge Augmentation

Acid Black 172 dye adsorption from aqueous solution by hydroxyapatite as low-cost adsorbent

The Acid Black 172 dye adsorption on the uncalcined hydroxyapatite nanopowder was investigated. The hydroxyapatite prepared by wet coprecipitation method has high specific surface area of 325 m2/g and crystal sizes smaller than 70 nm. The batch adsorption experiments revealed that under the optimum adsorption conditions (pH 3, hydroxyapatite dosage 2 g/L, initial dye concentration 400 mg/L and temperature 20 °C) the dye removal efficiency was 95.78% after 1 h of adsorption. The adsorption kinetics was best described by the pseudo-second order kinetic model. The intraparticle diffusion model shows that intraparticle diffusion is not the sole rate-limiting step; the mass transfer also influences the adsorption process in its initial period. The Langmuir isotherm model best represented the equilibrium experimental data, and the maximum adsorption capacity (q m ) was 312.5 mg/g.

A comparative study of two types of sternal pins used for sternal closure: poly-l-lactide sternal pins versus uncalcined hydroxyapatite poly-l-lactide sternal pins

Bioabsorbable poly-L-lactide (PLLA) sternal pins are applied to reinforce sternal closure during cardiac surgery. However, these pins lack osteoconductivity. A new bioabsorbable sternal pin with osteoconductivity, made of uncalcined hydroxyapatite and poly-L-lactide (u-HA-PLLA) has been developed. This study was conducted to compare the two types of sternal pins in terms of sternal stability and healing after median sternotomy. Between October 2006 and January 2012, 105 patients underwent aortic surgery for aortic aneurysms or dissection via median sternotomy and sternal closure with sternal pins. Among these patients, 75 were followed for 12months using serial computed tomography (CT). PLLA sternal pins were used in 30 patients (group A) and u-HA-PLLA sternal pins were used in 45 patients (group B). The incidence rates of transverse sternal dehiscence, anteroposterior displacement and complete sternal fusion were evaluated using CT. The cross-sectional cortical bone density area (CBDA) of the sternum around the sternal pins was examined to evaluate the osteoconductivity of the sternal pins. There were no significant differences between groups A and B in the sternal dehiscence rate (6.7 vs 4.4%), sternal displacement rate (6.7 vs 2.2%) or 12-month sternal fusion rate (63.3 vs 73.3%). The CBDA around the sternal pins significantly increased between discharge and 12months after surgery in group B (P<0.001) but not in group A. These results show that u-HA-PLLA sternal pins exhibit certain osteoconductivity; however, both PLLA and u-HA-PLLA sternal pins provide comparable clinical outcomes regarding sternal stability and healing.

FT-IR and XRD investigations on sintered fluoridated hydroxyapatite composites

Sintered fluoridated hydroxyapatite (FHA) composites were synthesized by calcination at 700 °C for 2 h. The phase changes of the sintered FHA composites have been studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The effects of the calcination temperature and the presence of calcium fluoride (CaF 2) on the sintered FHA composites were examined. The expanded (300) XRD reflections of sintered FHA composites were significantly different from the uncalcined hydroxyapatite (HA). The XRD reflection peaks of sintered FHA composites gradually shifted to a higher-angle direction when CaF 2 increased. The shift of peaks indicates the a-axis lattice parameter reduction as a result of the calcination process and the substitution of OH by F. The uncalcined composite materials were stable in OH vibrational groups and showed neither OH·F·OH nor OH·F hydrogen bonds. The sintered FHA composites showed FHA phase. With the increase of CaF 2 wt.%, the OH·F·OH and then OH·F hydrogen bonds of sintered FHA composites were forming.

Usefulness of Osteosynthesis Device Made of Hydroxyapatite-Poly-L-Lactide Composites in Port-Access Cardiac Surgery

Port-access minimally invasive cardiac surgery has been developed with the aim of reducing surgical invasion. We conduct port-access cardiac surgery, generally through an intercostal space. To ensure sufficient visual field, either the upper or lower rib may be divided. In the process of restoration of divided ribs, we have developed a bone fixation technique using a new osteosynthesis device by way of prevention of pseudoarthrosis. Forty-five consecutive patients underwent right-sided anterior intercostal thoracotomy under the port-access method between July 2006 and July 2007. We used a totally resorbable osteosynthesis device (Super Fixsorb; Takiron Co., Ltd., Osaka, Japan) consisting of a mix of poly-L-lactide (PLLA) and particulate resorbable uncalcined hydroxyapatite (u-HA). Fixation of the rib-costal cartilage was sufficiently achieved in this manner. No clinical symptoms suggestive of inflammation or infection were identified in the areas corresponding to the site of bone junction, and no patients have suffered pseudoarthrosis perioperatively and up to one year after surgery. Computed tomographic (CT) scanning clearly visualized these devices, and their attachment to the rib surfaces was confirmed in the patient who underwent CT scanning after the longest tested interval of 133 days after surgery. In this study, the possibility was suggested that the advantages of u-HA/PLLA composite, such as early osteoconductive property and bioactive property, might beneficially affect bone fusion. We conclude that this osteosynthesis device can be applied in various fields, including cardiovascular surgery, and that its use will contribute to improvement of patients' postoperative quality of life.

In vivo evaluation of a porous hydroxyapatite/poly‐DL‐lactide composite for bone tissue engineering

As reported previously, a porous composite of uncalcined hydroxyapatite (u-HA) and poly-DL-lactide (PDLLA) showed excellent osteoconductivity and biodegradability as a bone substitute in rabbit model. In this study, to investigate the usefulness of this composite as a scaffold loaded with cells, we estimated whether this material showed osteogenesis on implantation to extraosseous site. On loading with syngeneic bone marrow cells and implantation into rat dorsal subcutaneous tissue, osteogenesis with enchondral ossification was seen both on and in the material at 3 weeks after implantation. The osteogenesis in the u-HA/PDLLA had progressed, and newly formed bone tissue was found in the material by 6 weeks. To investigate the osteoinductive properties of the material, we implanted this porous composite material into extraosseous canine dorsal muscle. At 8 weeks, osteogenesis was seen in the pores of the material. Newly formed bone could be observed adjacent to the material. In addition, cuboidal osteoblasts adjacent to the newly formed bone were evident. Neither cartilage nor chondrocytes were found. These results might indicate that the material induced osteogenesis by intramembranous ossification. Conversely, similar porous PDLLA did not induce osteogenesis during the observation period. Therefore, porous HA/PDLLA, which has osteoconductive and osteoinductive properties, might be a useful material for use as a bone substitute and cellular scaffold.

Bioactive and bioresorbable cellular cubic-composite scaffolds for use in bone reconstruction

We used a novel composite fibre-precipitation method to create bioactive and bioresorbable cellular cubic composites containing calcium phosphate (CaP) particles (unsintered and uncalcined hydroxyapatite (u-HA), alpha-tricalcium phosphate, beta-tricalcium phosphate, tetracalcium phosphate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrate or octacalcium phosphate) in a poly-D/L-lactide matrix. The CaP particles occupied greater than or equal to 70 wt% (greater than or equal to 50 vol%) fractions within the composites. The porosities of the cellular cubic composites were greater than or equal to 70% and interconnective pores accounted for greater than or equal to 70% of these values. In vitro changes in the cellular geometries and physical properties of the composites were evaluated over time. The Alamar Blue assay was used to measure osteoblast proliferation, while the alkaline phosphatase assay was used to measure osteoblast differentiation. Cellular cubic C-u-HA70, which contained 70 wt% u-HA particles in a 30 wt% poly-D/L-lactide matrix, showed the greatest three-dimensional cell affinity among the materials tested. This composite had similar compressive strength and cellular geometry to cancellous bone, could be modified intraoperatively (by trimming or heating) and was able to form cortico-cancellous bone-like hybrids. The osteoinductivity of C-u-HA70, independent of biological growth factors, was confirmed by implantation into the back muscles of beagles. Our results demonstrated that C-u-HA70 has the potential as a cell scaffold or temporary hard-tissue substitute for clinical use in bone reconstruction.

Apatitic calcium phosphates used in compression: rationalization of the end-use properties

Different apatitic calcium phosphates used as direct compression excipients have been developed in the last years. The difficulty to obtain reproducible synthesis explains their approximative and irregular composition. TRI-TAB® commercial grade called anhydrous tricalcium phosphate is associated to a chemical formula corresponding to a mixture of tricalcium phosphate (Ca 3(PO 4) 2) and calcium hydroxide (Ca(OH) 2). The chemical analysis shows that it is hydroxyapatite (Ca 10(PO 4) 6(OH) 2). The purpose of this work is to rationalize the chemical and physical natures of apatitic calcium phosphates used in direct compression, and thus their technological properties. Apatitic calcium phosphates differing in their Ca/P molar ratio (from 1.500 i.e. tricalcium phosphate to 1.667 i.e. hydroxyapatite) have been synthesized and their compression properties have been analysed. The results have been compared to those of TRI-TAB®. They pointed out the importance of the chemical nature contribution. Tricalcium phosphate-based materials exhibited an excellent compactibility when not calcined. Uncalcined hydroxyapatite had similar properties than TRI-TAB®, that is intermediate. Calcined tricalcium phosphate and hydroxyapatite showed a low compaction ability. It appears that the perfect chemical and physical control of the material is important in particle design to rationalize and optimise the tablet formulation as well as the process.

Electrophoretic deposition of hydroxyapatite coatings on metal substrates : A nanoparticulate dual-coating approach

Hydroxyapatite coatings can be readily deposited on metal substrates by electrophoretic deposition. However, subsequent sintering is highly problematic owing to the fact that temperatures in excess of 1100°C are required for commercial hydroxyapatite powders to achieve high density. Such temperatures damage the metal and induce metal-catalysed decomposition of the hydroxyapatite. Furthermore, the firing shrinkage of the hydroxyapatite coating on a constraining metal substrate leads to severe cracking. The present study has overcome these problems using a novel approach: the use of aged nanoparticulate hydroxyapatite sols (lower sintering temperature) and a dual coating strategy that overcomes the cracking problem. Dual layers of uncalcined hydroxyapatite (HAp) powder were electrophoretically coated on Ti, Ti6Al4V and 316L stainless steel metal substrates, sintered at 875–1000°C, and characterised by SEM and XRD, and interfacial shear strength measurement. Dual coatings on stainless steel had an average high bond strength (about 23 MPa), and dual coatings on titanium and titanium alloy had moderate strengths (about 14 and 11 MPa, respectively), in comparison with the measured shear strength of bone (35 MPa). SEM and XRD demonstrated that the second layer blended seamlessly with the first and filled the cracks in the first. The superior result on stainless steel is attributed to a more appropriate thermal expansion match with hydroxyapatite, the thinner oxide layer, or a combination of these factors.